Two vessel reactor system and method for hydrolysis and digestion of wood chips with chemical enhanced wash method

Abstract

A reactor vessel system including: a first reactor vessel having a hydrolysate and liquid extraction screen, a first region above the extraction screen that is maintained at conditions promoting a hydrolysis reaction in the cellulosic material, a second region below the extraction screen in which the hydrolysis is substantially suppressed and a wash liquid inlet below the extraction screen providing wash liquid at a temperature below a hydrolysis temperature; a transport pipe having an inlet coupled to the first reactor vessel and an outlet coupled to a second reactor vessel, and the second reactor vessel includes a liquid discharge that extracts a portion of liquid from the second reactor vessel and directs the portion of liquid to the first reactor vessel or to the transport pipe.

What is claimed is: 
     
       1. A method to produce pulp from cellulosic material comprising:
 adding a liquid to a cellulosic material to form a slurry of the cellulosic material, wherein the liquid is at least one of water and a liquid extracted from an upper inlet of a first reactor vessel, and the liquid to the cellulosic material is substantially devoid of an acid; 
 pumping the slurry of cellulosic material to the upper inlet in the first reactor vessel; 
 hydrolyzing the cellulosic material in an upper region of the first reactor vessel by adding pressure and heat energy to the vessel, wherein the hydrolysis is conducted at a temperature of at least 150 degrees Celsius; 
 extracting hydrolysate from the cellulosic material through an extraction screen below the upper region and in the first reactor vessel; 
 introducing a wash liquid to a lower region of the first reactor vessel where the wash liquid suppresses hydrolysis of the cellulosic material in the lower region and said wash liquid flows upward through the cellulosic material to the extraction screen, wherein the wash liquid as introduced to the lower region has an amount of alkali chemicals of no more than five percent of the amount of cellulosic material in the first reactor vessel; 
 discharging the cellulosic material from a lower outlet of the first reactor vessel; 
 introducing the discharged cellulosic material to a second reactor vessel; 
 introducing cooking liquor into an upper region of the second reactor vessel to digest the cellulosic material to produce pulp; 
 extracting liquor from the second reactor vessel and introducing the extracted liquor into the lower region of the first reactor vessel, and 
 monitoring the pH of the extracted liquor and increasing a flow of wash liquid to the lower region if the monitored pH is above a predetermined pH level. 
 
     
     
       2. The method as in  claim 1  wherein the wash liquid includes an amount of at least one of sodium hydroxide and white liquor substantially without sulfur in a range of 0.01 percent to 5 percent of the amount of cellulosic material flowing through the first reactor vessel. 
     
     
       3. The method as in  claim 1  wherein the hydrolysis is conducted at a hydrolysis temperature in a range of 150° C. to 175° C. 
     
     
       4. The method as in  claim 1  wherein the wash liquid is 10° C. to 70° C. cooler than the hydrolysis temperature. 
     
     
       5. The method as in  claim 1  wherein the hydrolysis is conducted while the cellulosic material has a pH in a range of 1 to 6. 
     
     
       6. The method as in  claim 1  wherein the wash liquid when introduced to the lower region has a pH in a range of 3 to 7. 
     
     
       7. The method as in  claim 1  wherein the cellulosic material in the upper region is maintained at a temperature above a hydrolysis temperature to promote hydrolysis and the cellulosic material in the lower region is maintained at a temperature at least ten degrees Celsius below the hydrolysis temperature. 
     
     
       8. The method of  claim 1  wherein the hydrolysis temperature is at least 170 degrees Celsius. 
     
     
       9. The method of  claim 1  further comprising extracting liquor from the second reactor vessel and introducing the extracted liquor into the lower region of the first reactor vessel. 
     
     
       10. The method of  claim 1  further comprising adding steam to the first reactor vessel to pressurize the vessel and add heat energy to the vessel. 
     
     
       11. The method of  claim 1  wherein the wash liquid is a mixture of water and at least one of sodium hydroxide and white liquor substantially without sulfur, wherein the amount of the sodium hydroxide and white liquor is not more than five percent of the cellulosic material in the first reactor vessel. 
     
     
       12. A method to suppress hydrolysis of cellulosic material comprising:
 introducing cellulosic material in an upper inlet of a first reactor vessel, wherein the material moves downwardly through the first reactor vessel; 
 adding steam at above atmospheric pressure to the first reactor vessel; 
 maintaining at above a hydrolysis temperature the cellulosic material in an upper region of the first reactor vessel, wherein the temperature of the cellulosic material is maintained at least at 150 degrees Celsius; 
 while the cellulosic material is at the temperature of at least 150 degrees, hydrolyzing the cellulosic material; 
 extracting hydrolysate from the cellulosic material through an extraction screen below the upper region in the first reactor vessel; 
 adding a wash liquid to cool the cellulosic material below the extraction screen to a temperature below the hydrolysis temperature, wherein the wash liquid is at least one of water and a liquid extracted from an upper inlet of a the first reactor vessel; 
 discharging the cellulosic material from a bottom outlet of the first reactor vessel to a second reactor vessel, wherein a cooking liquor is first introduced to the cellulosic material after the cooling of the cellulosic material to a temperature below the hydrolysis temperature; 
 extracting liquor from the second reactor vessel and introducing the extracted liquor to a lower region of the first reactor vessel, and 
 monitoring the pH of the extracted liquor and increasing a flow of the wash liquid to the lower region if the monitored pH is above a predetermined pH level. 
 
     
     
       13. The method of  claim 12  wherein cooling the cellulosic material includes introducing the wash liquid to the lower region of the first reactor vessel and flowing the wash liquid upward to the extraction screen. 
     
     
       14. The method of  claim 12  wherein the wash liquid is a mixture of water and at least one of sodium hydroxide and white liquor substantially without sulfur. 
     
     
       15. The method of  claim 12  wherein the amount of the sodium hydroxide and white liquor is not more than five percent of the amount or cellulosic material in the first reactor vessel. 
     
     
       16. The method of  claim 12  wherein the hydrolysis temperature is at least 170 degrees Celsius. 
     
     
       17. The method of  claim 12  further comprising adding steam to an upper region of the first reactor vessel to pressurize the vessel and add heat energy to the vessel. 
     
     
       18. A method to produce pulp from cellulosic material comprising:
 adding a liquid to a cellulosic material to form a slurry of the cellulosic material, wherein the liquid is at least one of water and a liquid extracted from an upper inlet of a first reactor vessel, and the liquid to the cellulosic material is substantially devoid of an acid; 
 pumping the slurry of cellulosic material to the upper inlet in the first reactor vessel; 
 hydrolyzing the cellulosic material in an upper region of the first reactor vessel by adding pressure and heat energy to the vessel, wherein the hydrolysis is conducted at a temperature of at least 150 degrees Celsius, wherein the step of hydrolyzing the cellulosic material is performed without addition of an acid formed independently of the hydrolysis reaction to promote hydrolysis; 
 extracting hydrolysate from the cellulosic material through an extraction screen below the upper region and in the first reactor vessel; 
 introducing a wash liquid to a lower region of the first reactor vessel where the wash liquid suppresses hydrolysis of the cellulosic material in the lower region and said wash liquid flows upward through the cellulosic material to the extraction screen, wherein the wash liquid as introduced to the lower region has an amount of alkali chemicals of no more than five percent of the amount of cellulosic material in the first reactor vessel; 
 discharging the cellulosic material from a lower outlet of the first reactor vessel; 
 introducing the discharged cellulosic material to a second reactor vessel, and 
 introducing cooking liquor into an upper region of the second reactor vessel to digest the cellulosic material to produce pulp, wherein the cooking liquor from the second reactor vessel is absent from the cellulosic material in the first reactor vessel.